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Stefan Velikogne, Verena Resch, Carina Dertnig, Joerg H Schrittwieser, Wolfgang Kroutil
Imine reductases (IREDs) have recently become a primary focus of research in biocatalysis, complementing other classes of amine-forming enzymes such as transaminases and amine dehydrogenases. Following in the footsteps of other research groups, we have established a set of IRED biocatalysts by sequence-based in silico enzyme discovery. In this study, we present basic characterisation data for these novel IREDs and explore their activity and stereoselectivity using a panel of structurally diverse cyclic imines as substrates...
August 13, 2018: ChemCatChem
Felix Strieth-Kalthoff, Ashley R Longstreet, Jessica M Weber, Timothy F Jamison
Herein, we introduce a new class of bench-stable N -heterocyclic carbene (NHC) nickel-precatalysts for homogeneous nickel-catalysis. The nickel(II) complexes are readily activated to Ni0 in situ under mild conditions, via a proposed Heck-type mechanism. The precatalysts are shown to facilitate carbonyl-ene, hydroalkenylation, and amination reactions.
July 9, 2018: ChemCatChem
Yakub Fam, Thomas L Sheppard, Ana Diaz, Torsten Scherer, Mirko Holler, Wu Wang, Di Wang, Patrice Brenner, Arne Wittstock, Jan-Dierk Grunwaldt
Tomographic imaging of catalysts allows non-invasive investigation of structural features and chemical properties by combining large fields of view, high spatial resolution, and the ability to probe multiple length scales. Three complementary nanotomography techniques, (i) electron tomography, (ii) focused ion beam-scanning electron microscopy, and (iii) synchrotron ptychographic X-ray computed tomography, were applied to render the 3D structure of monolithic nanoporous gold doped with ceria, a catalytically active material with hierarchical porosity on the nm and μm scale...
July 9, 2018: ChemCatChem
Alina Filip, Emma Z A Nagy, Souad D Tork, Gergely Bánóczi, Monica I Toşa, Florin D Irimie, László Poppe, Csaba Paizs, László C Bencze
Tailored mutants of phenylalanine ammonia-lyase from Petroselinum crispum ( Pc PAL) were created and tested in ammonia elimination from various sterically demanding, non-natural analogues of phenylalanine and in ammonia addition reactions into the corresponding ( E )-arylacrylates. The wild-type Pc PAL was inert or exhibited quite poor conversions in both reactions with all members of the substrate panel. Appropriate single mutations of residue F137 and the highly conserved residue I460 resulted in Pc PAL variants that were active in ammonia elimination but still had a poor activity in ammonia addition onto bulky substrates...
June 21, 2018: ChemCatChem
Thierry K Slot, David Eisenberg, Gadi Rothenberg
We consider the factors that govern the activity of bifunctional catalysts comprised of active particles supported on active surfaces. Such catalysts are interesting because the adsorption and diffusion steps, which are often discounted in "conventional" catalytic scenarios, play a key role here. We present an intuitive model, the so-called "active doughnut" concept, defining an active catalytic region around the supported particles. This simple model explains the role of adsorption and diffusion steps in cascade catalytic cycles for active particles supported on active surfaces...
May 24, 2018: ChemCatChem
Filip Sebest, Jay J Dunsford, Matthew Adams, Jeremy Pivot, Paul D Newman, Silvia Díez-González
A series of well-defined copper(I) complexes bearing ring-expanded N-heterocyclic carbene (NHC) ligands has been applied to the azide-alkyne cycloaddition reaction. The obtained results notably showed that the six-membered NHC ligands outperform well-established five-membered ones. [CuI(Mes-6)] displayed a remarkable catalytic activity while respecting the strict criteria for click reactions.
May 9, 2018: ChemCatChem
Dogukan H Apaydin, Hathaichanok Seelajaroen, Orathip Pengsakul, Patchanita Thamyongkit, Niyazi Serdar Sariciftci, Julia Kunze-Liebhäuser, Engelbert Portenkirchner
We report on a self-assembled system comprising a molecular copper-porphyrin photoelectrocatalyst, 5-(4-carboxy-phenyl)-10,15,20-triphenylporphyrinatocopper(II) (CuTPP-COOH), covalently bound to self-organized, anodic titania nanotube arrays (TiO2 NTs) for photoelectrochemical reduction of oxygen. Visible light irradiation of the porphyrin-covered TiO2 NTs under cathodic polarization up to -0.3 V vs. Normal hydrogen electrode (NHE) photocatalytically produces H2 O2 in pH neutral electrolyte, at room temperature and without need of sacrificial electron donors...
April 24, 2018: ChemCatChem
Niko M Kinnunen, Matthew Keenan, Kauko Kallinen, Teuvo Maunula, Mika Suvanto
Catalytic combustion of methane, the main component of natural gas, is a challenge under lean-burn conditions and at low temperatures owing to sulfur poisoning of the Pd-rich catalyst. This paper introduces a more sulfur-resistant catalyst system that can be regenerated during operation. The developed catalyst system lowers the barrier that has restrained the use of liquefied natural gas as a fuel in energy production.
April 9, 2018: ChemCatChem
Wouter S Lamme, Jovana Zečević, Krijn P de Jong
The effects of the metal deposition and activation methods on metal particle size and distribution were investigated for carbon nanotube supported Pd catalysts. The Pd precursor was loaded by incipient wetness impregnation, ion adsorption, and deposition precipitation and was activated by thermal treatment under a nitrogen atmosphere or in the liquid phase by reduction by formaldehyde or sodium borohydride. Regardless of the metal precursor loading method, activation under a N2 atmosphere at 500 °C led to homogeneously distributed 4 nm Pd particles...
April 9, 2018: ChemCatChem
Annika Bernhardt, Harald Kelm, Frederic W Patureau
An 17 O NMR spectroscopy survey of more than 100 ubiquitous organic solvents and compounds, including some typical oxofluorinated solvents such as hexafluoroisopropanol, trifluoroethanol, trifluoroacetic acid, and others, is presented with D2 O as a reference. A strong alternating α,β-CF3 -substituent chemical shift effect was thus observed. This alternating deshielding-shielding effect is suspected to have a role in the exceptional properties of these oxofluorinated solvents, notably in oxidative cross-coupling reactions...
April 9, 2018: ChemCatChem
Ilse M Denekamp, Martijn Antens, Thierry K Slot, Gadi Rothenberg
We study the allylic oxidation of cyclohexene with O2 under mild conditions in the presence of transition-metal catalysts. The catalysts comprise nanometric metal oxide particles supported on porous N-doped carbons (M/N:C, M=V, Cr, Fe, Co, Ni, Cu, Nb, Mo, W). Most of these metal oxides give only moderate conversions, and the majority of the products are over-oxidation products. Co/N:C and Cu/N:C, however, give 70-80 % conversion and 40-50 % selectivity to the ketone product, cyclohexene-2-one. Control experiments in which we used free-radical scavengers show that the oxidation follows the expected free-radical pathway in almost all cases...
March 7, 2018: ChemCatChem
Baira Donoeva, Petra E de Jongh
Colloids with controlled dimensions, morphology and composition can be used to obtain supported metal catalysts with desired characteristics. Yet, removal of capping agents which block active metal sites in such catalysts can be challenging: mild methods often result in incomplete removal of capping agents, whereas harsher methods can cause change in particle size or morphology or cause metal segregation for bimetallic particles. Here we provide evidence that polyvinylpyrrolidone used as a stabilizing agent for gold colloids is present both on the metal and the support surface after colloid deposition on the TiO2 support...
March 7, 2018: ChemCatChem
Kaituo Liu, Xiaoming Huang, Evgeny A Pidko, Emiel J M Hensen
The catalytic hydrogenation of lactic acid to 1,2-propanediol with supported Ru catalysts in water was investigated. The influence of catalyst support (activated carbon, γ-Al2 O3 , SiO2 , TiO2 , and CeO2 ) and promoters (Pd, Au, Mo, Re, Sn) on the catalytic performance was evaluated. Catalytic tests revealed that TiO2 yields the best Ru catalysts. With a monometallic Ru/TiO2 catalyst, a 1,2-propanediol yield of 70 % at 79 % lactic acid conversion was achieved at 130 °C after 20 h reaction. Minor byproducts of the hydrogenation reaction were propionic acid, ethanol, 1-propanol, and 2-propanol...
February 21, 2018: ChemCatChem
Ryan Oozeerally, David L Burnett, Thomas W Chamberlain, Richard I Walton, Volkan Degirmenci
Heterogeneous catalysts are desired for the conversion of glucose, the most abundant sugar in renewable biomass, but presently their synthesis requires highly toxic chemicals with long synthesis times. We report the conversion of glucose into fructose and 5-hydroxymethylfurfural on a heterogeneous catalyst that is stable and selective and operates in the most environmentally benign solvent, water. We used a bifunctional solid with Lewis and Brønsted acid sites by partially replacing the organic linker of the zirconium organic framework UiO-66 with 2-monosulfo-benzene-1,4-dicarboxylate...
February 21, 2018: ChemCatChem
Wesley Böhmer, Tanja Knaus, Francesco G Mutti
The amination of alcohols is an important transformation in chemistry. The redox-neutral (i.e., hydrogen-borrowing) asymmetric amination of alcohols is enabled by the combination of an alcohol dehydrogenase (ADH) with an amine dehydrogenase (AmDH). In this work, we enhanced the efficiency of hydrogen-borrowing biocatalytic amination by co-immobilizing both dehydrogenases on controlled porosity glass FeIII ion-affinity beads. The recyclability of the dual-enzyme system was demonstrated (5 cycles) with total turnover numbers of >4000 and >1000 for ADH and AmDH, respectively...
February 2018: ChemCatChem
Rolf Beerthuis, Liang Huang, N Raveendran Shiju, Gadi Rothenberg, Wei Shen, Hualong Xu
Catalytic biomass conversion is often hindered by coking. Carbon compounds cover active surface and plug pores, causing catalyst deactivation. Material design at the nanoscale allows tailoring of the catalytic activity and stability. Here, we report a simple synthesis of nanosized ZSM-5 materials by using a silicalite-1 seeding suspension. ZSM-5 crystals were grown from a deionized silica source in the presence of ammonia. By using silicalite-1 seeds, crystalline ZSM-5 is synthesized without any structure-directing agent...
January 9, 2018: ChemCatChem
Wei Chen, Bart Zijlstra, Ivo A W Filot, Robert Pestman, Emiel J M Hensen
The way in which the triple bond in CO dissociates, a key reaction step in the Fischer-Tropsch (FT) reaction, is a subject of intense debate. Direct CO dissociation on a Co catalyst was probed by 12 C16 O/13 C18 O scrambling in the absence and presence of H2 . The initial scrambling rate without H2 was significantly higher than the rate of CO consumption under CO hydrogenation conditions, which indicated that the surface contained sites sufficiently reactive to dissociate CO without the assistance of H atoms...
January 9, 2018: ChemCatChem
Edwin S Gnanakumar, Wesley Ng, Bilge Coşkuner Filiz, Gadi Rothenberg, Sheng Wang, Hualong Xu, Laura Pastor-Pérez, M Mercedes Pastor-Blas, Antonio Sepúlveda-Escribano, Ning Yan, N Raveendran Shiju
We report a facile and general approach for preparing ultrafine ruthenium nanocatalysts by using a plasma-assisted synthesis at <100 °C. The resulting Ru nanoparticles are monodispersed (typical size 2 nm) and remain that way upon loading onto carbon and TiO2 supports. This gives robust catalysts with excellent activities in both organosilane oxidation and the oxygen evolution reaction.
November 23, 2017: ChemCatChem
Sakilam Satishkumar, Suresh Poudapally, Prasanna K Vuram, Venkateshwarlu Gurram, Narender Pottabathini, Dellamol Sebastian, Lijia Yang, Padmanava Pradhan, Mahesh K Lakshman
In this work we have assessed reactions of N 6 -([1,1'-biaryl]-2-yl)adenine nucleosides with Pd(OAc)2 and PhI(OAc)2 , via a PdII /PdIV redox cycle. The substrates are readily obtained by Pd/Xantphos-catalyzed reaction of adenine nucleosides with 2-bromo-1,1'-biaryls. In PhMe, the N 6 -biarylyl nucleosides gave C6-carbazolyl nucleoside analogues by C-N bond formation with the exocyclic N 6 nitrogen atom. In the solvent screening for the Pd-catalyzed reactions, an uncatalyzed process was found to be operational...
November 9, 2017: ChemCatChem
Lingqian Meng, Xiaochun Zhu, Brahim Mezari, Robert Pestman, Wannaruedee Wannapakdee, Emiel J M Hensen
The influence of framework substituents (Al3+ , Ga3+ , Fe3+ and B3+ ) and morphology (bulk vs. nanometer-sized sheets) of MFI zeolites on the acidity and catalytic performance in the methanol-to-hydrocarbons (MTH) reaction was investigated. The Brønsted acid density and strength decreased in the order Al(OH)Si>Ga(OH)Si>Fe(OH)Si≫B(OH)Si. Pyridine15 N NMR spectra confirmed the differences in the Brønsted and Lewis acid strengths but also provided evidence for site heterogeneity in the Brønsted acid sites...
October 23, 2017: ChemCatChem
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